1. The black deposit found in the stomatal pits of certain conifers, and thought to be soot, was found to be a natural product of the leaf. 2. The substance in the stomata of juniper, fir, and Austrian pine was found to be a wax. 3. The wax is finely granular, permeable to gases, but must greatly retard gas exchange and thus retard metabolism and water loss. 4. There is a remarkable parallel between presence of the wax and xerophytism in the conifers, and between absence of the wax and mesophytism (and hygrophytism). 5. No relation is seen to exist between wax in the stomata and the high sensitiveness of certain conifers to smoke, except that as a factor inducing xerophytism the wax may lower the resistance of the tree.